Proteoglycan synthesis and metabolism by mouse uterine stroma cultured in vitro

Chondroitin sulfate proteoglycans (CSPGs) and hyaluronate have been identified as the predominant glycoconjugates synthesized and secreted by mouse uterine stromal cells (USC) cultured in vitro. CSPGs in both the cell-associated and secreted fractions have identical characteristics with regard to anion exchange chromatographic behavior, sensitivity of the intact molecules and constituent glycosaminoglycans to a variety of chemical and enzymatic digestions, lack of interaction with hydrophobic affinity resins, and density (greater than 1.46 g/ml). Chase labeling studies indicated a metabolic half-life of cell-associated, [35S]sulfate-labeled macromolecules of 5-6 h. Once secreted, CSPGs did not appear to be degraded or endocytosed to a significant extent. In contrast, a large fraction (50%) of the cell-associated CSPGs were degraded to low Mr (less than 3000) products via a chloroquine-sensitive pathway. Studies of the kinetics of intracellular transport indicated that approximately 30 min were required for CSPG core proteins to move from the rough endoplasmic reticulum to the Golgi apparatus and 15-20 min to move from the Golgi to the cell surface, i.e. protease-accessible compartment. There was no significant lag period between the time CSPGs first arrived at the cell surface and the time at which they were first detectable in the medium. Examination of CSPG expression during USC differentiation in utero or in vitro demonstrated that these molecules were produced with similar efficiency by USC under both conditions. Collectively, these studies provide the first comprehensive description of proteoglycan production and metabolism in USC, a uterine cell type intimately involved with embryo implantation processes. Potential functions for CSPGs and hyaluronate as modulators of embryo invasive processes and uterine expansion are proposed.